EARTH 20 Lecture Notes - Lecture 8: Pumice, Volcanic Ash, Volcanic Glass
Document Summary
Basalt (least viscous) > andesite > rhyolite (most viscous) Temperature: higher temperature, lower viscosity (heat it up, it flows more easily and gets thinner) Solubility of dissolved gases decreases as pressure decreases. As magma rises out of mantle, the pressure decreases and gases start to leak out of magma: rapid volume increase > explosivity of a volcano. Co2 comes out of liquid in gas form (volume increases due to decrease in pressure when cap is taken off) At great depth: dissolved gas still has high solubility, so no bubbles. Pressure decreases as magma rises through mantle (starts to form bubbles) Volcanic ash: frothy, silicated magma segments that cool. Water (like basalt): same volatiles, low viscosity > bubbles come to surface level, not explosive. Pasta sauce (like andesites and rhyolites): same volatiles, higher viscosity > bubbles push to surface level, often explosive when they surface. Exceptions:continental hotspots where rhyolites can erupt explosively)
